The standard most often cited for pedestal decks never mentions pedestals

BS 8579:2020 is a British Standard published by BSI, and it carries the status of a guide rather than a specification or a code of practice. A guide sets out principles and recommendations for a subject, and the standard states this of itself in its own scope.

What reading it actually costs

The text is paywalled. Seeing the clauses in full means buying the document from BSI, so a reference to BS 8579 in a specification or a design statement is often a reference to a title and a scope someone has seen described second-hand.

The word that is not there

Search the full text for pedestal and nothing comes back. BS 8579:2020 covers design for balconies and terraces as a subject. It does not name height-adjustable support pedestals, as a product, a build-up layer or a detail, anywhere in its text.

A citation to BS 8579 attached to a pedestal deck requirement is, on that basis, a citation to a document that never discusses the thing being specified.

A specifier searching for the standard on pedestal decks tends to land on BS 8579, because it sits in the paving and decking section of most library catalogues. The rules that actually govern a build-up live somewhere else, each in a document written for a different job.

Fire classification

Which route a balcony qualifies for is set out in Approved Document B, the guidance that accompanies the Building Regulations, together with the statutory instrument it supports. That is a question about reaction to fire and soffit construction, and a paving standard does not reach it. Read the two routes on Pedestal Deck Regulations UK — Two Compliance Routes.

Imposed load

The load a deck has to carry comes from the Eurocode for actions on structures and its UK National Annex. A manufacturer's own datasheet figure sits alongside that, tested to whatever standard the manufacturer chose, and the two are not always the same thing measured the same way.

Slab thickness, spacing and overhang

How far a slab can span between pedestals and overhang its last support is a question about the paving unit itself, answered by the product standard that covers that slab type together with the supplier's own tolerances. See Slab Thickness, Spacing and Overhang for Pedestal Decks for where that figure does and does not exist in writing.

Falls, drainage and access to the membrane

Falls and drainage are covered by warranty-body guidance and drainage-industry guidance notes written specifically for terraces. Access to the waterproofing below the deck is a separate question again, usually answered by whoever wrote the outlet detail. See Access to the Waterproofing Membrane Under a Pedestal Deck.

Where a specification cites BS 8579 for one of these points, ask the author which clause they are relying on. If they cannot point to a clause, the figure came from somewhere else and was attributed to the wrong document.